1. Related Art Statement
The present invention relates to wear resisting steel, a sliding member for a cylinder in an internal combustion engine, and a ring spring, and more particularly, to high performance wear resisting steel, a sliding member for a cylinder in an internal combustion engine, and a ring spring wherein the wear resisting steel has excellent resistance to wear and scuffing, provides greater strength and greater elongation than cast iron and greater toughness than ultrahigh strength steel or sintered hard alloy, and also provides good machinability.
A piston ring used in an internal combustion engine such as a diesel engine requires properties and characteristics such as wear resistance and anti-scuffing. Conventionally, flake graphite cast iron (hereinafter, referred to as "cast iron") such as Uballoy (trade mark of JAPAN PISTON RING CO., LTD), ultrahigh strength steel with greater hardness, and sintered hard alloy are well known as wear resisting material for such a purpose.
However, cast iron has disadvantages of poor strength and low elongation, and ultrahigh strength steel and sintered hard alloy have also disadvantages of poor toughness, and poor machinability.
By the way, a ring spring is used for a stretcher of a leveler for rolled steel sheets. Since the ring spring requires relatively high strength and toughness, spring steel is conventionally used for the ring spring.
2. Object and Summary of the Invention
It is a first aim of the present invention to provide wear resisting steel having stable anti-scuffing property and a sliding member for a cylinder made of the wear resisting steel.
A ring spring made of conventional material is damaged on its sliding surface so that its life-time is quite short.
It is a second aim of the present invention to keep the characteristics of the ring spring for a long period without considerable damage so as to lengthen product life.
Wear resisting steel according to the present invention consists of:
carbon: equal to or less than 2.2% by weight; silicon: equal to or less than 1.2% by weight; manganese: equal to or more than 0.2% by weight and less than 1.20% by weight, chromium: equal to or less than 16% by weight; phosphorus: equal to or less than 0.08% by weight; sulfur: equal to or more than 0.15% by weight and less than 0.60% by weight; other compositions: equal to or less than 2.0% by weight; and the balance substantially comprising of iron.
The ranges of compositions of preferred wear resisting steels (No. 1 through No. 4) are listed in the following Table 1.
TABLE 1 __________________________________________________________________________ (wt %) No. of Steel C Si Mn Cr P S others Fe __________________________________________________________________________ No. 1 .ltoreq.2.2 .ltoreq.1.2 1.20 .gtoreq. 0.2 .ltoreq.16 .ltoreq.0.08 0.60 .gtoreq. 0.15 .ltoreq.2.0 bal. No. 2 .ltoreq.2.2 .ltoreq.1.2 1.20 .gtoreq. 0.2 .ltoreq.6.0 .ltoreq.0.08 0.60 .gtoreq. 0.15 .ltoreq.2.0 bal. No. 3 0.25.about.2.0 0.20.about.1.20 0.40.about.1.20 0.80.about.5.50 .ltoreq.0.05 0.20.about.0.50 .ltoreq.1.0 bal. No. 4 0.60.about.2.0 0.10.about.0.40 0.40.about.1.0 11.0.about.15.0 .ltoreq.0.05 0.20.about.0.60 .ltoreq.1.0 bal. __________________________________________________________________________
For the following reasons, the compositions of No. 1 steel are limited as shown in Table 1.
C&gt;1.8 (means "C exceeds 1.8% by weight", hereinafter, signs are used in the same manner), Si&gt;1.2, P&gt;0.08, or Cr&gt;16 makes the mechanical properties (material strength, elongation) poor. Particularly, C&gt;2.2 makes the elongation remarkably poor. S&lt;0.15, Mn&lt;0.2 (less than 0.2 % by weight) make the sliding properties (anti-scuffing) poor.
It should be noted that Cr.ltoreq.6.0 (6.0% by weight or less) such as No. 2 steel improves the mechanical properties.
No. 3 steel and No. 4 steel both offer a good balance between the mechanical properties and the sliding properties thereof.
A sliding member for a cylinder in an internal combustion engine and a ring spring according to the present invention are made of the wear resisting steel as described above.
It is preferable that the surface of the wear resisting steel is sulphurized by electrolysis or is treated by baking molybdenum dioxide after electrolyte sulphurizing.
The sliding member for a cylinder in an internal combustion engine according to the present invention may be a piston ring, a cylinder liner, or a piston skirt.
The ring spring of the present invention comprises inner rings and outer rings wherein at least sliding surfaces of the inner rings and/or outer rings are made of the aforementioned wear resisting steel. Employing the wear resisting steel for the ring spring keeps up the good spring property of the ring spring for long periods, thereby extending the ring spring's life.
The numbers of the inner and outer rings of the ring spring, the inner diameters and so on are not limited. Lubricant (for example MoS.sub.2 grease) is preferably applied on the sliding surfaces between the inner rings and the outer rings.
The wear resisting steel, the sliding member for a cylinder in an internal combustion engine and the ring spring according to the present invention are generally sulphurized after being processed by the following normal heat treatment before use. Laser heat treatment or subzero treatment may be employed besides the following heat treatment.
Method of heat treatment and conditions
Heating (temperature: 780-840 .degree. C.).fwdarw.Quenching in oil.fwdarw.Tempering (temperature: 200-600 .degree. C.).fwdarw.Air cooling.
The sulphurizing according to the present invention is conducted to form a sulphurized layer (iron sulfide Fe.sub.x S) on the surface of the steel by the electrochemical reaction (ionic reaction) by soaking the steel in molten salt in a vessel to electrolyze the steel as anode with the counter electrode as cathode.
It is enough to form the sulphurized layer of 10 .mu.m or less, normally 3-9 .mu.m, preferably 5-8 .mu.m in depth.
The wear resisting steel of the present invention has excellent resistance to wear and scuffing, provides greater strength and greater elongation than cast iron and greater toughness than ultrahigh strength steel or sintered hard alloy, and also provides good machinability.
The wear resisting steel of the present invention is particularly industrially useful as a material of a sliding member for a cylinder in an internal combustion engine such as a piston ring, a cylinder liner, or a piston skirt, and a ring spring.